Surface Fed Air
It had always been an annoying fact that by using conventional tanks we were always limted by the air supply as to how long we could attend the work face of the wreck site, and when working hard moving bolders and digging down to the bedrock air consumption seems to go through the roof even at the relativly shallow depths of 7-10 metres at which we work. Not to mention the lack of mobility suffered by having a large air tank strapped to your back.
We had tried conventional surface supply methods such as standard petrol powered generators etc, but found the high noise levels and constant worry of fumes and fire risk aboard a small inshore boat a major concern, and decided to look into a smaller, safer solution. To this end a couple of the team (Chris and Bob) went about designing their own test system to initially see if their was any milage in investing some hard earned cash in one of the 12 volt systems that are so popular in the warmer diving waters around the world such as Australia and the USA.
After some creative engineering with a couple of air tanks, some hose, a few fittings and a rather nervous test diver, some success was acheived. The system was based around two 15 litre tanks in the boat with the air line running from there to the diver. After overcoming a few small hitches, the sinking and kinking of the airline, it work reasonably well allowing the diver the extra dive time of a twin 15 litre set with none of the inconvenience of having it on your back. This was enough to convince a few of us that this was definitly the way to go.
After some investigation via the Internet a couple of likely candidates were found. In the end we chose the systems on offer from PowerDive International in Australia. Mainly designed for boat maintenance and recreational diving they seemed the perfect fit for the type of shallow inshore diving required on the Halsewell wreck.
Seadart divers now use two of the proucts available, one is a boat mounted system whilst the other floats on the surface and follows the diver below, although we tend to tie it up to one of the boats due to the proximity of the cliff face. Both units run from 12 volt batteries with breathing hose and demand valves connected to each. The benefits have been well worth the investment, allowing divers far greater dive times, more freedom underwater and much less kit to haul in and out of boats.
We have of course received a few funny looks from the diving crowd that frequent Swanage and a few disapproving stares as we put our trust in these new fangled contraptions, but we just quietly smile back as they struggle down to the end of the pier almost bent double under the stain of their own tanks.